Placental pericytes: the initial characterization shows similarities, as well as peculiar differences, with mesenchymal stem/stromal cells.

Pericytes (PCs) represent a unique type of contractile cells surrounding the endothelium of small blood vessels, identified and described firstly in late 18th century. Since then, several studies revealed that these cells are not only involved in blood vessel architecture, but exert various angiogenic functions. From recent literature, it has been suggested that blood vessels harbor also perivascular native ancestors of the mesenchymal stem cells (MSCs) that, depending on the anatomy of the vessel, can be classified as pericyte- or adventitial-derived MSCs. MSCs are a heterogeneous population of cells with extensive proliferative capacity and differentiation potential. Human MSCs have been initially isolated and characterized from bone marrow as plastic adherent fibroblast-like cells carrying a peculiar phenotype identified by co-expression of specific CD markers. Nevertheless, following studies identified cells with similar properties in various tissues including muscle, skin and adipose tissue. We have previously analyzed several biological properties of plastic adherent CD105+/CD90+/ CD73+/CD45- cells isolated from subcutaneous and visceral adipose tissues, identifying the lack of osteogenic differentiation in cells isolated from omental tissue. Since omentum is a highly vascularized mass, our finding raised the possibility that the isolated cell line was mainly composed by PCs rather than MSCs. To address this clue we isolated PCs from highly vascularized human placenta and we are in process of comparing the biological properties of the two cell lines. We initially performed immunohistochemistry assays on paraffin- or OCT-embedded placental sections to confirm the presence and abundance of microvascular cell types as indicated by specific stainings. Then, fresh human placenta samples were collected, the chorionic villi portions were minced into small pieces, digested with collagenase and the cell suspension was seeded in M199 medium containing 20% FBS and 1% penicillin/streptomycin solution. After 2-3 days non-adherent cells were removed and the complete medium was replaced twice a week until cellular confluence. Adherent cells were morphologically analyzed daily and, at confluence, trypsinized, expanded, and subjected to qPCR, immunofluorescence, and flow cytometry analyses. Preliminary results indicate similarities as well as peculiar differences, between MSCs and placental-derived PCs, thus expanding the range of cells of mesenchymal origin that share some of the properties of MSCs.